Fuel cell stacks typically consist of a plurality of fuel cells connected in series through a load. Each fuel cell has a number of components including: a cathode and an anode with an electrolyte disposed therebetween, a cathode chamber, and an anode chamber. Around each fuel cell component is a frame. Within the fuel cell, a fuel, such as hydrogen, and an oxidant, such as oxygen, react to produce electricity.
For example, in an alkaline fuel cell, which typically operates at atmospheric pressure and temperatures between 140.degree. F. and 250.degree. F., hydrogen reacts with oxygen to form water, heat, and electricity. At the cathode, water, free electrons, and oxygen react to form hydroxide ions. The hydroxide ions migrate through the electrolyte to the anode. At the anode the hydroxide ions react with hydrogen to produce water, heat, and electricity. In these fuel cells, a strong aqueous solution of potassium hydroxide serves as the electrolyte.
Typically, the fuel and oxidant enter the respective chambers within the fuel cell through passages in the frames which surround the various components. Since direct contact between the fuel and oxidant (usually hydrogen and oxygen) can cause an explosion, it is extremely important to prevent leakage between the passages. Additionally, since potassium hydroxide is a strong caustic and toxic if inhaled, it is also very important that it be carefully sealed within the fuel cell.
Presently, two sealants are conventionally employed to prevent leakage within or out of fuel cells; a rubber sealant and an epoxy coated fabric sealant. Both sealants require a labor intensive application, are expensive, and require a thick frame (a problem where volume and weight are limited), with the rubber seal also requiring an additional molding step.
The epoxy coated fabric is used to provide an edge seal 5 to the frame 1 (FIG. 1) and to form the frame of the electrode assembly by manual interleaving the electrodes 12, matrix 14, and electrolyte reservoir plate 16 between layers of epoxy-coated fabric and bonding these components to the frame with heat and pressure.
With respect to the rubber sealant, a rubber adhesive (A; see FIG. 2) is placed in a groove 20 located in the frame 25 of the component. An extruded bead of uncured rubber B is then placed in the groove. The rubber is compressed and heated to form a specific shape as is shown in FIG. 2. Once the rubber has been molded, the frames are fitted together. Generally, during maintenance of the fuel cell, when the components are separated the rubber pulls out of the groove, requiring the molding process to be repeated prior to reassembling the fuel cell.
What is needed in the art is a sealant for use in fuel cells which is convenient to use, inexpensive, does not require the use of a thick frame, is dependable, and which can be used in a potassium hydroxide environment.
The present invention discloses a sealant which can be used in a fuel cell to prevent leakage between component frames. This sealant, which is comprised of an essentially homogeneous mixture of about 50 wt% to about 90 wt% butyl rubber and about 10 wt% to about 50 wt% ethylene propylene latices, can be used in a caustic environment and at elevated temperatures.
Also disclosed is a fuel cell which utilizes said sealant as claimed. The sealant is used to prevent leakage of the fuel, oxidant, reaction products, and in some cases the electrolyte.
The foregoing and other features and advantages of the present invention will become more apparent from the following description and accompanying drawings.